We have shown that non-pancreatic lipases account for the digestion of 20-40% of dietary fat, and that their activity is probably not confined only to the stomach, but may continue in the small intestine. Furthermore, whereas in the rat, lingual lipase is the only non-pancreatic digestive lipase, in man fat digestion in the stomach may be catalyzed by two enzymes, lingual and gastric lipases. Our studies also show that gastric lipase is present in several other species (dog, guinea pig, baboon) and that is the only non-pancreatic digestive lipase in the rabbit. Therefore, we shall investigate the following the human subjects: 1. The characteristics of purified human lingual and gastric lipases. 2. The quantitative contribution of these two enzymes to intragastric lipolytic activity in the newborn premature and full term infant. 3. The effect of sucking on the quantitative contribution of the two enzymes to the lipolytic activity present in the stomach. The animal models for these studies will be the developing rabbit and dog, species with only or high activity of gastric lapase, respectively. Furthermore feeding patterns, milk fat composition and lipase activity differ in these two species in a way that can provide the data necessary to evaluate the role of lingual and gastric lipases in the fat digestion of formula or breast fed preterm infants. We will investigate: 1. The developmental profile of gastric lipase in the suckling rabbit and of gastric and lingual lipases in the suckling puppy. 2. Detailed characterization of gastric lipase during the developmental period: substrate specificity, stability to conditions prevailing in the stomach (low pH, pepsin) and small intestine (bile salts, proteolytic enzymes). 3. The cellular source of gastric lipase: are lipase and pepsin, the two digestive enzymes secreted by the gastric mucosa, secreted by the same cell type? 4. Quantitation of in vivo lipolysis and fat absorption in the newborn and the contribution of non-pancreatic lipases to this process.